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Old 05-19-2018, 10:45 AM   #1
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Generator to Run Refrigerator and AC

I am posting this question for my Dad who recently purchased his first motorhome. He was told to use his gas powered generator to run his AC and refrigerator instead of running his AC through his engine and refrigerator on propane. What is the best configuration?
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Old 05-19-2018, 10:49 AM   #2
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Well, his engine will run his cab A/C but not his rooftop AC unit which requires shore power or the generator to run. His reefer can usually run on LP gas or shore power, if that is what he has.
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Old 05-19-2018, 10:56 AM   #3
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Well, his engine will run his cab A/C but not his rooftop AC unit which requires shore power or the generator to run. His reefer can usually run on LP gas or shore power, if that is what he has.

That makes sense. He was told to run his rooftop AC and not his cab AC to save gas. Is this true?
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Old 05-19-2018, 11:18 AM   #4
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That makes sense. He was told to run his rooftop AC and not his cab AC to save gas. Is this true?
No, not true at all. Engine-driven A/C will use less gas than running a generator to power a larger, higher-power-demanding A/C unit. Running the generator to power the fridge is also going to waste much more gas because the fridge doesn't run 100% of the time once up to temp. So there are periods of time where the generator will be running and powering nothing, wasting gas.

There's no escaping the laws of thermodynamics, either. Simply put, turning the A/C compressor and powering the blower fan takes less energy than running a generator and powering a large A/C unit.

Keep the fridge on LP until connected to shore power.

The only time I would run the generator and roof A/C while driving down the road is if the dash A/C is unable to keep us cool enough. If the dash A/C is keeping us cool then there is no reason to run the generator and roof A/C.
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Old 05-19-2018, 11:18 AM   #5
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sgreats, welcome to the forum to your dad. Engine powered AC compressor load is less of a factor on MH gas mileage with the big engines they have. The Onan 4000 uses approx 1/2 gal per hour. Greater factors on mileage are hills, speed, winds, proper tire pressure, weight, towing...... We run dash air most of the time with the fridge on propane, but donít hesitate to crank up the gen to keep the back at a comfortable temperature.
Something else to consider. If it is hot outside and you are running the gen and roof air, you will already have a cool coach when you stop for the night. If you let the coach get hot during the day and then pull in for the night and turn on the roof air, it will take much much longer for the temperature to become comfortable.
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Old 05-19-2018, 11:23 AM   #6
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That makes sense. He was told to run his rooftop AC and not his cab AC to save gas. Is this true?
That may or may not he true. Too many variables.
The chassis A/C does create a parasitic draw on the engine which in turn causes fuel consumption. How much? Itís probably close to the amount the genset will use. But consider that you(he) will save propane by running the fridge on AC. Again, not a lot. Then there is the maintenance on the genset... and so on.
So the conventional wisdom points to doing what is more comfortable. After all, that is the point is it not?
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Old 05-19-2018, 11:43 AM   #7
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That makes sense. He was told to run his rooftop AC and not his cab AC to save gas. Is this true?

Running the generator requires more fuel, gas or propane, than the OEM chassis cab A/C will ever use. I don't even see a noticeable MPG difference when running the Ford A/C on my ScanGuage. The old days of engine driven A/C units having a huge impact on gas mileage are long gone.

A easy trick to help keep the cab area cooler, or warmer, is to hang a full length curtain behind the seats. That keeps the cool, or hot, air up front and helps muffle some of the noises while driving. Plus my wife likes the look of nice curtains blocking off the cab area while we're parked....
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Old 05-19-2018, 11:49 AM   #8
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Something else to consider. If it is hot outside and you are running the gen and roof air, you will already have a cool coach when you stop for the night. If you let the coach get hot during the day and then pull in for the night and turn on the roof air, it will take much much longer for the temperature to become comfortable.
I've found that running the gen set and RV A/C for the last hour or so of driving works pretty well cooling down the coach. I've done it both ways, all day long and last hour, and the comfort level is about the same...
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Old 05-19-2018, 01:57 PM   #9
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Comfort vs Gas Savings

Sgreats,

As several have said the generator option is going to use more gas than the dash AC. However, comfort to me trumps fuel economy (if it didn't I'd be driving a Prius and camping in a tent).

I live in Oklahoma and here, Texas, New Mexico, and other high sunshine locations, my dash AC will keep the driver and front seat passenger comfortable till the outside temp hits 90 degrees then I need to add the roof top cooling capacity. If I have passengers in the back, then I have to add the roof top cooling almost all the time. So to me it isn't which one will save more gas but which solution will satisfy my need for comfort and then which solution is the most economical.

I have a residential refrigerator that runs off my battery or the generator so I can't speak to your propane refrigerator but if I were to "guess", I would probably say if the generator is already running then run it on the generator and save the propane for when you have to use propane

The most important part is have fun and enjoy the ride the way you want to, not what I tell you (or anyone else).

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Old 05-19-2018, 02:00 PM   #10
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First question... what year and model of rig does he have? Does it have a residential fridge or the RV gas/electric model? If he is worried about gas mileage he bought the wrong thing!

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Old 05-19-2018, 02:14 PM   #11
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X2 what wahoonc said
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Old 05-19-2018, 02:49 PM   #12
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I am posting this question for my Dad who recently purchased his first motorhome. He was told to use his gas powered generator to run his AC and refrigerator instead of running his AC through his engine and refrigerator on propane. What is the best configuration?
The dealer might also have some information we don't.

We have a friend who always runs the rooftop a/c on a generator to keep the children in the motorhome cool. The cab a/c isn't enough.

If he's trying to conserve propane or doesn't want to worry about turning it off and on when he pulls into gas stations, it would make sense to run both on the generator and just leave the propane off.
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Old 05-20-2018, 11:15 AM   #13
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Just a note about genny usage. It is recommended that the unit be run for half an hour or so every 30 days at half load or more. Running the roof A/C is the perfect way to do this while on the road.
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Old 05-20-2018, 11:24 AM   #14
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I'd simply run whatever is necessary to keep the rig as cool as you'd like.
Worrying about the few dollars one way or the other for fuel mileage on a trip is moot.

As for the fridge... he should run it on whatever he is most comfortable with. Although perfectly acceptable, many don't like using propane fueled appliances when traveling.
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Old 05-20-2018, 07:31 PM   #15
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This is all great information assuming you are not talking about when you are parked and camping.
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Old 05-21-2018, 11:31 AM   #16
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Hi Scott, I was trying to private message you and I Couldnít seem to send out..
My husband and I just moved into Englewood also this past January .... and I noticed that weíre neighbors and FROG
Members... just wanted to say hi.
Pat and Dennie Holbrook
My name is Palmtreepat
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